Magnetic storage systems, including data storage devices such as hard disk drives, are used to store large amounts of information. A magnetic head in a magnetic storage system typically includes read and write transducers for retrieving and storing magnetically encoded information on a magnetic recording medium, such as a disk.
In a disk-drive system, the read and write transducers reside in a slider that flies over the recording media (e.g., a disk). As storage densities have increased, and slider fly-heights have decreased, the fly-height of the slider-to-disk spacing has become smaller. Lubricant pickup, corrosion, electrical breakdown, electrostatic discharge (ESD) can all negatively affect the fly-height of the slider. The negative effects can be mitigated or eliminated by controlling the slider's voltage potential with respect to the disk's potential. Controlling the slider's voltage reduces slider wear and allows for lower flying-heights.
Data storage devices, such as hard disk drives, can suffer from radio-frequency interference (RFI). The slider body can transfer these RFI signals to the read transducer, which could damage the read transducer or interfere with read data signals.
The need to increase storage densities has led to the development of technologies such as microwave-assisted magnetic recording (MAMR). In MAMR systems, a spin-torque oscillator (STO) comprising a field-generation layer (FGL) and spin-polarization layer (SPL) is placed within in the write gap, and a bias current is supplied to the STO. In operation, the write head generates a write field that, beneath the main pole, is substantially perpendicular to the magnetic recording layer, and the STO generates a high-frequency auxiliary field to the recording layer. Ideally, the auxiliary field has a frequency close to the resonance frequency of the magnetic grains in the recording layer to facilitate the switching of the magnetization of the grains. As a consequence, the oscillating field of the STO's FGL resonates with the media and provides strong writing. In addition, the STO's auxiliary field may also be used for write field enhancement with the STO mounted near the write head's pole tip.
To generate the auxiliary write field, the STO requires the application of a bias voltage that affects the write transducer's pole potential. In prior-art systems, this bias voltage is DC. Furthermore, the bias voltage is currently not utilized for controlling the slider's potential with respect to the disk's potential. Previous proposals for controlling the potential of the slider used a dedicated line or shared lines such as a contact sensor, which has limited functionality through a common-mode control. There is an ongoing need for methods and apparatuses that control the slider's voltage potential with respect to the disk's potential while supplying a bias current to a STO in the write gap.